The DMSP satellite is still operating, but the SSM/I sensor is not
Regular readers will recall that on Feb 16th I blogged about this graph of arctic sea ice posted on the National Snow and Ice Data Center sea ice news page. The downward jump in the blue line was abrupt and puzzling.
Click for larger image
Today NSIDC announced they had discovered the reason why. The sensor on the Defense Meteorological Satellite Program (DMSP) satellite they use had degraded and now apparently failed to the point of being unusable. Compounding the bad news they discovered it had been in slow decline for almost two months, which caused a bias in the arctic sea ice data that underestimated the total sea ice by 500,000 square kilometers. This will likely affect the January NSIDC sea ice totals.
Figure 1. High-resolution image Daily Arctic sea ice extent map for February 15, 2009, showed areas of open water which should have appeared as sea ice. Sea Ice Index data. About the data. Please note that our daily sea ice images, derived from microwave measurements, may show spurious pixels in areas where sea ice may not be present. These artifacts are generally caused by coastline effects, or less commonly by severe weather. Scientists use masks to minimize the number of “noise” pixels, based on long-term extent patterns. Noise is largely eliminated in the process of generating monthly averages, our standard measurement for analyzing interannual trends. Data derived from Sea Ice Index data set.
Figure 2.
High-resolution imageDaily total Arctic sea ice extent between 1 December 2008 and 12 February 2009 for Special Sensor Microwave/Imager SSM/I compared to the similar NASA Earth Observing System Advanced Microwave Scanning Radiometer (EOS AMSR-E) sensor. —Credit: National Snow and Ice Data Center
Dr. Walt Meier of NSIDC had planned to do a guest post here on WUWT, but this evening, with the magnitude of the problem looming, he’s asked to defer that post until later. I certainly can’t fault him for that. He’s got his hands full. Hopefully they have a contingency plan in place for loss of the sensor/space platform. I applaud NSIDC for recognizing the problem and posting a complete and detailed summary today. I’ve resposted it below in its entirety. Note that this won’t affect other ice monitoring programs that use the Advanced Microwave Scanning Radiometer (EOS AMSR-E) sensor, which is on an entirely different platform, the AQUA satellite.
UPDATE: 2/19 Walt Meier writes with a clarification: “One detail, though perhaps an important [one]. I realize that it is bit confusing, but it is just one channel of the sensor that has issues. And it isn’t so much that it “failed”, but that quality degraded to the point the sea ice algorithm – the process to convert the raw data into sea ice concentration/extent – failed on Monday.” – Anthony
From NSIDC Sea Ice News:
As some of our readers have already noticed, there was a significant problem with the daily sea ice data images on February 16. The problem arose from a malfunction of the satellite sensor we use for our daily sea ice products. Upon further investigation, we discovered that starting around early January, an error known as sensor drift caused a slowly growing underestimation of Arctic sea ice extent. The underestimation reached approximately 500,000 square kilometers (193,000 square miles) by mid-February. Sensor drift, although infrequent, does occasionally occur and it is one of the things that we account for during quality control measures prior to archiving the data. See below for more details.
We have removed the most recent data and are investigating alternative data sources that will provide correct results. It is not clear when we will have data back online, but we are working to resolve the issue as quickly as possible.
Where does NSIDC get its data?
NSIDC gets sea ice information by applying algorithms to data from a series of Special Sensor Microwave/Imager (SSM/I) sensors on Defense Meteorological Satellite Program (DMSP) satellites. These satellites are operated by the U.S. Department of Defense. Their primary mission is support of U.S. military operations; the data weren’t originally intended for general science use.
The daily updates in Arctic Sea Ice News & Analysis rely on rapid acquisition and processing of the SSM/I data. Because the acquisition and processing are done in near-real time, we publish the daily data essentially as is. The data are then archived and later subjected to very strict quality control. We perform quality control measures in coordination with scientists at the NASA Goddard Space Flight Center, which can take up to a year. High-quality archives from SSM/I, combined with data from the earlier Scanning Multi-channel Microwave Radiometer (SMMR) data stream (1979–1987) provide a consistent record of sea ice conditions now spanning 30 years.
Data error sources
As discussed above, near-real-time products do not undergo the same level of quality control as the final archived products, which are used in scientific research published in peer-reviewed journals. However, the SSM/I sensors have proven themselves to be generally quite stable. Thus, it is reasonable to use the near-real-time products for displaying evolving ice conditions, with the caveat that errors may nevertheless occur. Sometimes errors are dramatic and obvious. Other errors, such as the recent sensor drift, may be subtler and not immediately apparent. We caution users of the near-real-time products that any conclusions from such data must be preliminary. We believe that the potential problems are outweighed by the scientific value of providing timely assessments of current Arctic sea ice conditions, as long as they are presented with appropriate caveats, which we try to do.
For several years, we used the SSM/I sensor on the DMSP F13 satellite. Last year, F13 started showing large amounts of missing data. The sensor was almost 13 years old, and no longer provided complete daily data to allow us to track total daily sea ice extent. As a result, we switched to the DMSP F15 sensor for our near-real-time analysis. For more information on the switch, see “Note on satellite update and intercalibration,” in our June 3, 2008 post.
On February 16, 2009, as emails came in from puzzled readers, it became clear that there was a significant problem—sea-ice-covered regions were showing up as open ocean. The problem stemmed from a failure of the sea ice algorithm caused by degradation of one of the DMSP F15 sensor channels. Upon further investigation, we found that data quality had begun to degrade over the month preceding the catastrophic failure. As a result, our processes underestimated total sea ice extent for the affected period. Based on comparisons with sea ice extent derived from the NASA Earth Observing System Advanced Microwave Scanning Radiometer (EOS AMSR-E) sensor, this underestimation grew from a negligible amount in early January to about 500,000 square kilometers (193,000 square miles) by mid-February (Figure 2). While dramatic, the underestimated values were not outside of expected variability until Monday, February 16. Although we believe that data prior to early January are reliable, we will conduct a full quality check in the coming days.
Sensor drift is a perfect but unfortunate example of the problems encountered in near-real-time analysis. We stress, however, that this error in no way changes the scientific conclusions about the long-term decline of Arctic sea ice, which is based on the the consistent, quality-controlled data archive discussed above.
We are actively investigating how to address the problem. Since we are not receiving good DMSP SSM/I data at the present time, we have temporarily discontinued daily updates. We will restart the data stream as soon as possible.
Some people might ask why we don’t simply switch to the EOS AMSR-E sensor. AMSR-E is a newer and more accurate passive microwave sensor. However, we do not use AMSR-E data in our analysis because it is not consistent with our historical data. Thus, while AMSR-E gives us greater accuracy and more confidence on current sea ice conditions, it actually provides less accuracy on the long-term changes over the past thirty years. There is a balance between being as accurate as possible at any given moment and being as consistent as possible through long time periods. Our main scientific focus is on the long-term changes in Arctic sea ice. With that in mind, we have chosen to continue using the SSM/I sensor, which provides the longest record of Arctic sea ice extent.
For more information on the NSIDC sea ice data, see the following resources on the NSIDC Web site:
- Sea Ice Index
- Why is the Sea Ice Index product used to study sea ice?
- Do your data undergo quality control?
Anthony. I do not wish to belabour the point about the missing Canadian cities on the National weather map, but I look at the map everyday to get an idea how patterns of warm and cold move around over the American continent. I cannot recall ever seeing the Canadian stations missing. That is why I mentioned it. I did not think that Canada or the US had seceded from each other!
Dr Meier, I look forward to your posting here. I’m glad that we seem to be gradually cracking the issues that have led to so much irresponsible reporting on scary non-existent Arctic melt scenarios – at least, with regard to data integrity. I hope to see issues of media science reporting integrity, following on the heels of this.
Everyone, if you want some basic understanding of the Polar regions and the questionable Steig Antarctica paper and its 10-year genesis, enjoy Warming Antarctica by Paintwork and the rest of the page. We are all still learning.
Clive (23:21:02) :
Since water has vastly greater thermal capacity than air the air temperature can safely be reckoned to depend on water temperature over any reasonable expanse of ocean (as we know well in the UK). Therefore although land air temperatures are indeed cold enough to freeze brass monkeys, let alone water, I’d guess that the arctic ocean could be “warm” due to currents, etc. and thus lead to less sea ice forming.
Good work all round on this story.
On February 16, 2009, as emails came in from puzzled readers, it became clear that there was a significant problem
Kudos to ICECAP and WUWT. Citizen scientist bloggers discovered and reported the erroneous readings. That is pretty cool. Thanks to the Internet, science is becoming a more public undertaking, a less esoteric and hidden away in laboratories process. That’s the trend, anyway, and it’s a very healthy one, IMHO.
Thank you, Anthony, for being a leader in this new wave, this new gestalt of science.
Thanks for actively moderating this thread, Anthony!
The http://www.swpc.noaa.gov/SolarCycle/ sunspot graph has been updated. — John M Reynolds
In the description of the sensor systems, they are described
as passive. I wonder why they don’t use a Multi Frequency
Synthetic Aperture Radar? SAR systems are very good at
seeing density differences regardless of weather, and with
the addition of CCD (coherent change detection) processing
they could yield some incredible animations. With Interferometric
Synthetic Aperture Radar and CCD processing you could watch
the ice grow and retard in 3D.
Sorry, this is a link to Wikipedia, but you’ll get the Idea!
http://en.wikipedia.org/wiki/Interferometric_synthetic_aperture_radar
From NSIDC “We stress, however, that this error in no way changes the scientific conclusions about the long-term decline of Arctic sea ice, which is based on the the consistent, quality-controlled data archive discussed above.”
For sure, when the error is this way… doesn’t change anything for them.
Do step changes in the past data suggest a change in Artic weather, as originally thought, or does it now indicate problems with the satellite intrumentation?
I know from exerience that equipment that suffers a catastrophic failure usually have a history of periodic problems leading up to that failure.
It may also be worth checking the algorithms to see how they handle problematic sensors.
There is lesson here for all of us. Whenever doing a calculation if the answers are what one expects one tends to accepts them without checking; if they are not what you expect you check them. In this case NSIDC were expecting lower areas of Arctic sea ice and accepted the values for a long time. If the error had gone the other way, and showed higher areas of sea ice, we can be sure they would have been checked much sooner.
I would like to thank NSIDC and Dr Walt Meier for his candid explanation. Kudos.
I shall be watching the mainstream media with interest to look for erroneous reports of massive ice shrinkage beyond summer norms from now on with a better and more informed perspective.
Would there be any reason to suspect that increase in cosmic rays is going to lead to increased sensor erratica and/or failure?
i.e. – should we expect spaceborne sensors to show increased rates of failure?
“However, we do not use AMSR-E data in our analysis because it is not consistent with our historical data. Thus, while AMSR-E gives us greater accuracy and more confidence on current sea ice conditions, it actually provides less accuracy on the long-term changes over the past thirty years. There is a balance between being as accurate as possible at any given moment and being as consistent as possible through long time periods.”
It’s of course understandable that using as many different data sources as possible enhances QA abilities and general data reliability within this field of science – thus in Meier’s obvious interest to keep the DMSP based data collection going.
Otherwise the statement is odd – very odd.
something worth blogging about
“on February 15, 1979, global sea ice area was 16.79 million sq. km and on February 15, 2009, global sea ice area was 15.45 million sq. km. Therefore, global sea ice levels are 1.34 million sq. km less in February 2009 than in February 1979. This decrease in sea ice area is roughly equal to the area of Texas, California, and Oklahoma combined.
It is disturbing that the Washington Post would publish such information without first checking the facts.”
I remember that recently there was a discussion about the way coastlines have been redefined and this has led to a reduction in the area counted as sea ice. Has anyone come up with figures to compensate for changing definitions?
Off topic (sorry) but I think important.
One of the alarmists’ oft’ repeated claims is that methane can provide a positive feedback mechanism. The earth warms: methane is released from the permafrost and elsewhere: methane is a GHG: more warming occurs: more methane is released….
The earth emits radiation in the long-wave band between 4 and 50 microns with a peak at around 12 microns. Methane absorbs radiation in a narrow band around 7 to 8 microns. Almost no radiation in this band escapes at present so extra methane would have negligible warming effect.
Am I missing something or is this correct?
Neo-
While it may have been related to sensor malfunction, there is no question that there was a very strong and stable Southerly airstream through and to the West of the Norwegian Sea, which brought unseasonably warm air North, for a considerable period. This was caused by a stable High over North West Europe and Scandinavia, holding off a deep low in the Greenland area.
Perhaps a combination of both?
I am pleased that the (rather obvious in terms of effect on data) malfunctioning has been recognised, but sad that we may have lost an important data source. All good wishes to Dr. Meier and his colleagues in their endeavors to overcome this problem.
well, I suppose the data doesn’t really matter anymore…
E.P.A. Expected to Regulate Carbon Dioxide
http://www.nytimes.com/2009/02/19/science/earth/19epa.html
this ought to be great for the economy! /sarc
I’ve noticed sea level charts have been updated:
http://sealevel.colorado.edu/current/sl_noib_global.jpg
I was wondering if this will be commented on soon.
Normally sea levels spike at the end of the year, and then drop at midyear. Can we expect a drop in the months ahead?
On the side, Ipersonally I wouldn’t mind if Anthony limited the comments to 500 words or something. I wonder how many really long comments actually get read. On this thread though, readers seem to be keeping them short.
I was certain that it was a mistake that they would find and kindly fix. Otherwise, the graph would be a proof of James Hansen’s tipping points, if not death trains. 😉
More quantitatively, the sea ice anomaly has never been decreasing for 1 month even by 30% of the amount/rate that was shown on the blue graph line. Such a tripling of the record rate of decrease would be a 5-sigma effect or so.
The null hypothesis that it was a fluke would be ruled out according to the conventional statistical criteria of verification in science.
i am wondering what other sensors are degrading. Could it be more of the same for other systems. There is also a possibility of feed back as well..
There is a feeling that technology is stable, when it isnt as stable as it seems.
I’d like to apologise for the cheap shots I took in the recent-related thread.
But with the shenanigans we’ve seen from other circles, e.g. hockey stick, Antarctica, etc., I admit I got carried away, and the last time I shot from the hip without thinking. But no excuses.
With the media, institutions, bloggers, etc. diligently watching climate data, I’d still like to see institutions exercise far greater care in verifying data before making it public. The NSIDC’s disappearance of 1 million sq. km of ice should have thrown up a red flag. I still think they have to be more careful. It really does get down to their integrity.
All too often do the media run with “alarming news”, and then ignore subsequent corrections. This leads to public disinformation and bad policymaking. Personally I’m tired of paying through the nose for policy that’s based on junk data and panicked populations. For some of us, the nerves are getting a raw.
So, I guess it turns out this was indeed worth blogging about…
Check out earlier posts, this has been discussed a few times. This graph gives a more accurate view of trend with the seasonal signals removed and the inverse barometer applied. http://sealevel.colorado.edu/current/sl_ib_ns_global.jpg
I stopped looking at the NSIDC data a long time ago because I stopped trusting it…and maybe unfairly so.
But Leon makes a good point about the statement:
“There is a balance between being as accurate as possible at any given moment and being as consistent as possible through long time periods.”
So someone please tell me if my distrust is unfair.
It is openly admitted that the data is not accurate.